xe2x80x9cDistributed Wind Power Assessmentxe2x80x9d, February 2001, National Wind Coordinating Committee, Washington D.C.
xe2x80x9cAds Put Profit in Wind Powerxe2x80x9d, Popular Mechanics, June, 2001, page 20
Wind energy conversion systems, as currently deployed, are horizontal axis turbines mounted atop towers. It has been found that there is some economy of scale as well as other advantages such as lower incidence of avian mortality and less obtrusive acoustic noise output in deploying very large units of 1.5 megawatt or even larger capacities. However, out of necessity, these are usually part of large centralized xe2x80x9cwind farmsxe2x80x9d with dedicated electrical transmission lines. Local construction of turbine blades and towers are almost required because of the difficulty of transporting the physically large sections. Often access roads to remote sites must be built for transporting the turbine and tower sections as well as for the cranes and large rigging equipment required for erection and repairs. Distributed wind power installations must use smaller turbine units which are designed to interface with existing or upgraded distribution networks at lower voltages. The rural environments compatible with distributed wind power often do not have three-phase AC distribution which is a requirement for even modest (eg.xe2x80x9450 kw) units. Needless to say, high population density areas and high buildings in urban environments, while having adequate distribution networks and ready markets, are not a good match to a technology using towers (which also precludes their attachment to existing structures due to large moment loads and vibration). No known wind energy systems are compatible with the direct generation of other forms of secondary revenue streams.
In considering extraction of energy from natural water flow such as streams, tidal flow, or river currents, the sequestering of flow behind dams or barriers has traditionally been required. This incurs large outlays of capital, and often substantial environmental impact to man and to marine life. Pressure changes and sharp rotating blades within commonly used hydro turbines are themselves a danger to fish fry. The installations for hydroelectric plants or tidal generating facilities are generally permanent and unmovable fixtures.
This invention introduces the notion of a long-stroke open-channel reciprocating engine as an alternative to the turbines presently used to extract energy from the flow of water or air. Certain features of this type of reciprocating engine are analogous to other well known reciprocating engines such as steam or internal combustion engines. For example, the functions of pistons, crankshaft, valves, and connecting rods have direct counterparts while the cylinder, a flow confining element, has no counterpart in this xe2x80x9copen-channelxe2x80x9d engine. The engine of this invention uses drogue chutes to engage water currents or airfoils to engage wind in a manner analogous to pistons. Tethers of strong fibers such as nylon or aramid attach the drogue chutes or airfoils to a periodically reversing power drum which is turned when tether unwinds, not unlike the interaction of connection rods and crankshaft. Since this is a long-stroke engine, the power drum will turn multiple revolutions during one engine stroke. Valves have a direct counterpart in control of the drogue chutes or airfoils as they are purposely switched from a high pull mode (high drag and/or lift) to a low pull mode (low drag and/or lift) or vice-versa at the end of a stroke. As in other engines with a single piston, the most simple version has a single drogue chute or airfoil which extracts mechanical energy from fluid flow as it unwinds tether from the power drum in high pull mode and then must be wound back on the power drum while in low pull mode using parasitic energy; this is a xe2x80x9csingle-actingxe2x80x9d engine which extracts net positive energy over a complete cycle, but only on alternate strokes. Slightly more complex, an engine of this invention using two drogue chutes or airfoils can extract net positive energy from fluid flow on each stroke (ie.xe2x80x94xe2x80x9cdouble-actingxe2x80x9d) since one element is always in high-pull mode while the other is in low-pull mode reversing their respective roles at the end of each stroke. The extracted mechanical energy results from the difference in pull forces between the high-pull element unwinding tether from the power drum and the low-pull element being rewound onto the power drum. The parasitic loss is still there, but the power produced is almost continuous except for the brief pause at the end of each stroke during mode switching.
For water flow applications, the reciprocating engine of this invention can extract power directly from flow without sequestering it behind barriers or dams. In fact, an engine of this invention can be simply suspended below a moored barge. A system using a single drogue chute can follow rapidly shifting water currents without entanglement. Systems using a pair of drogue chutes can better extract energy from flowing water currents where rapid direction shifts are not a problem. The cyclic opening and closing of soft fabric structures such as drogue chutes at ambient pressure pose no threat to aquatic life; such movement is also conducive to self-cleaning from encrustation as from barnacles. The fact that very large drogue chutes can be deployed at very modest capital outlay compared to that of erecting and maintaining permanent civil works for alternate approaches implies lower system costs are indicated. Note that the systems of this invention for water applications are portable; they can be moved seasonally to optimize power generation or to accommodate other seasonal uses of a particular water area.
The advantages for wind energy conversion systems of this invention over traditional wind turbines are many. One important factor is that no towers are required. Heavy base equipment such as power transmissions and generating equipment is at ground level where it can be safely maintained without climbing towers. No very large elements are needed for this invention. Even large capacity systems can be transported over normal roads or even taken up elevators and erected on building roofs since no moment loading is involved and vibration is controlled as for any large mechanical device by known techniques. Using two self-buoyant helium or hydrogen inflated airfoils or a pair of non-buoyant fabric airfoils such as flexifoils attached to buoyant aerostats, the airfoils are simply suspended in the air regardless of the amount of wind. When wind picks up, the airfoils will synchronously reciprocate by virtue of mechanisms which adjust their angle of attack to control lift and/or drag to produce low pull and high pull modes as needed. Because of the inherent safety factors and lack of towers, these systems would be more easily integrated in populated commercial or industrial areas where adequate distribution lines exist and markets for generated electric power are in the local vicinity. Thus, the wind systems of this inventions are ideal for distributed wind energy in urban environments. Because of their integration with populated areas and the opportunity available by virtue of highly visible areas on the airfoils or their aerostats, the display of commercial logos or advertising messages can constitute a second revenue stream to enhance the profitability of such wind energy systems. Besides the urban deployment, other unique factors enhance the suitability of these wind systems where wind turbines with towers cannot compete. These systems can be deployed in hurricane prone areas since the airfoils can just be reefed at ground level and secured in case of impending storms. Small systems are so compact that they can even be back-packed and instantly deployed for camping use or for powering scientific instruments in remote windy areas. Similarly, they can be used on pleasure craft or recreational vehicles. Major wind farm installations off-shore can be simply installed on moored barges, no permanent towers below water level need be erected. On a grand scale, special airfoil designs with xe2x80x9csuper-tethersxe2x80x9d can be used to extract power from the jet stream. For wind farm applications, it may be possible to locate these systems in non-picturesque areas with good wind resource that would be prohibitive to harvest due to the high towers that would be necessary with conventional wind turbines. With these systems, airfoil height is simply a function of the length of a tether.
For water pumping applications on farms, it is possible to erect simple single airfoil systems that even use non-buoyant techniques by employing a tall light weight tower that just supports an airfoil at its lowest stroke position if the wind ceases to blow. This type of system can be built locally of indigenous materials. Buoyant techniques would eliminate the need for even this light weight tower. In either case, no power drum is necessary if reciprocating motion can be used directly for powering a reciprocating pump. Simple techniques for valving of the single airfoil can be implemented using an auxiliary tether from ground level, or these systems can use a self-regulating wind turbine powered mechanism situated aloft adjacent to the airfoil. This mechanism would cyclically adjust the airfoil in high-pull and low-pull modes as long as the wind is blowing. The difference in pull force would operate the water pump in a reciprocating fashion. These systems for water pumping save money in erection costs and first costs by eliminating the high cost of towers used by conventional water pumping windmills.